"Where have the space gone?" feature

[KOLANICH]

1 a user triggers a FS scan
2 the app scanns the fs and records exacts sizes of each file into a db alongside with its hash and some metadata. Let's call it "a snapshot".
3 the user creates an another snapshot
4 snapshots are stored in a differential way saving space
5 A user selects a pair of snapshots, the app computes their diff and shows to a user sorting by size difference.
6 there should be a way to create a snapshot and compare it to the previous one without involving any storage. This is needed because
a) the internal storage may have 0 (ZERO) bytes of free space and to free it it is crucial to understand what have eaten it
b) and doesn't inflict flash wear